Thesis advisor: John P. Christianson / Patients with posttraumatic stress disorder (PTSD) often show impaired ability to discriminate between “danger” and “safety” cues. Women are more than twice as likely to be diagnosed with PTSD as compared to men; however, translational research has largely relied on the use of male subjects despite evidence of sex differences in fear-motivated behaviors. Serotonergic activity, originating in the dorsal raphe nucleus (DRN) of the central nervous system (CNS), has been found to modulate fear discrimination in males and may contribute to sex differences observed in a Pavlovian fear discrimination paradigm. In this study, male and intact female Sprague-Dawley rats were exposed to fear conditioning with (CS+/CS-) or without (CS+) a safe conditioned stimulus, then subsequently sacrificed for immunohistochemical analysis of serotonergic activity via quantification of tryptophan hydroxylase (TPH) and Fos in the DRN. Females exhibited more rapid and robust discrimination between the CS+ danger cue and CS- safety cue as compared to males. Regardless of condition, females had more double-labeled TPH+Fos cells compared to males, but males had larger variation in TPH+Fos expression compared to females. A parabolic function for TPH+Fos counts predicted fear discrimination in males, but not females, reinforcing the view that serotonin is a modulator of safety-related behavior in males. / Thesis (BS) — Boston College, 2018. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Arts and Sciences Honors Program. / Discipline: Biology.

Thesis advisor: John P. Christianson / Accurate discrimination between safety and danger is necessary for survival, but is aberrant in individuals with post-traumatic stress disorder (PTSD). Despite its clinical relevance, very little is known about the cognitive and neural processes that underlie safety learning. Understanding how cues become safety signals is critical to understanding the impairments in fear modulation observed in individuals with PTSD. PTSD is more prevalent in women than men, and while research on sex differences in safety learning is limited, there is substantial evidence that males and females acquire and utilize safety signals differently. The aim of this dissertation is to describe behavioral sex differences in learning and recall of fear discrimination and explore the neural circuitry that allows this discrimination to occur. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Psychology.

Thesis advisor: John P. Christianson / Trauma and exposure to extreme stressors greatly increases a person’s vulnerability to developing mental illnesses like post-traumatic stress disorder (PTSD). Patients with PTSD often have impaired fear and safety learning, and despite the fact that women are more than twice as likely to develop PTSD, much of the research on this disorder has relied on the use of male subjects. This paper will review potential contributors to the sex differences seen in PTSD and fear-related learning. Our group has found that female rats show greater fear discrimination abilities than their male counterparts, but show no difference in levels of safety learning. Analysis of specialized extracellular matrix structures called perineuronal nets (PNNs) revealed that females displayed a much higher density of PNNs in the basolateral amygdala (BLA) than males, but not in the prefrontal cortex (PFC). / Thesis (BS) — Boston College, 2017. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Psychology.